1. Technical Field of the Invention
This invention relates to a tray for an integrated circuit or large scale integrated circuit (hereinafter referred to jointly as an IC), more particularly, to an IC tray having a small water absorption, a low surface resistance, and in some cases a low specific gravity, but having an excellent heat resistance with little change after prolonged storage.
2. Description of the Related Art
In the prior art a plate tray having a large number of product housing portions comprising, for example, concave groove portions formed thereon, is used for holding and conveying an IC during the baking (heat curing) of an encapsulating material such as epoxy resin molding compound in the final step of the IC production line, and the packaging step subsequent to that step.
There are two kinds of such trays, one made of a metal such as stainless steel or aluminum and the other made of a plastic such as polystyrene or polypropylene to which an electroconductivity has been imparted; the former is used in the heat curing step of the above encapsulating material and the latter is used in the product packaging step.
These prior art techniques, however, have problems such as a poor heat resistance and a lowering of the working efficiency of the process. To solve these problems, an IC tray based on a phenol resin is now under development, and is partly disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 61-285241 and 61-287951. The trays disclosed in these specifications, although having an excellent heat resistance, are defective from the viewpoint of impact resistance and specific gravity. The present inventors made various investigations into these problems and developed an IC tray by which they were solved.
The above IC tray developed by the inventors is characterized by having a low surface resistance, particularly a low specific gravity of 1.45 or less, and an excellent heat resistance with little deformation after heating. This IC tray is molded from a phenol resin molding comprising a natural fibrous filler and electroconductive carbon black added in a matrix comprising a resol type phenolic resin and an acrylonitrile-butadiene type rubber.
Nevertheless, the IC tray comprising this material, although having excellent initial characteristics, had different problems of warp generation and changes in dimensions due to expansion. These changes became extreme after prolonged storage at room temperature atmosphere (e.g., after 3 months in a room temperature atmosphere). Note, if these changes in the IC tray are, it is difficult to set an IC on tray by a robot, and thus the IC tray is practically useless. Further, if trays having an IC set thereon are stacked for storage, where an extreme change occurs, gaps are formed between the IC trays, and thus the IC is not completely fixed thereon.
For the reasons given above, although it depends on the shape and the size of the IC tray, IC manufactures are currently performing a strict quality control by setting management standard values of 1 mm or less for warping and a dimensional change rate of 0.15 to 0.20% in the case of products usually shaped as plates.